I wouldn't buy anything heavy from a place like Amazon. All that shipping makes zero sense to me!
I like to shop locally. If you don't feel you know what you are doing, making friends with the employees of a local garden center is your absolutely best bet.
In shopping at big stores, I look at their corporate culture. Do they give money to causes or political candidates I loathe? Do they pay their employees so little that they set up food donation stations for customers to support the workers? Then I don't line that owner's pockets. So personally, I do not shop in Walmart or Home Depot. But for supplies, they're all equivalent. Dirt is dirt, so potting soil is potting soil. You might save a few bucks at Lowe's over the local garden center, but you won't always get great advice on the planting. So if all your plants die, you'd have been better off paying a little more. If your garden center is more based on the gift shop model, you might pay more for pots and decorative stuff, so you can look around for those. I buy at different places, watching the sales.
Another advantage to your local places is free advice. I stop by a combination organic farm/garden center with a gift shop option off to the side. Besides enjoying supporting local, family-run businesses, I needed advice because of something wrong with one of my shrubs. I cut off a piece of it and sealed it in a zipper plastic bag. I showed it to the owner (I did not open it so that whatever disease it had didn't infect his stock!) and he was able to look right through the clear bag and tell me I had 2 problems (scale and thrips). He sent me right over to the counter with the organic spray that would treat both problems. Saved me an expensive shrub!